/*
 * @Description: 
 * @Author: Hongyang_Yang
 * @Date: 2020-08-31 18:34:57
 * @LastEditors: Hongyang_Yang
 * @LastEditTime: 2020-08-31 18:38:10
 */
/*
 * @lc app=leetcode.cn id=341 lang=cpp
 *
 * [341] 扁平化嵌套列表迭代器
 */

// @lc code=start
/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Return true if this NestedInteger holds a single integer, rather than a nested list.
 *     bool isInteger() const;
 *
 *     // Return the single integer that this NestedInteger holds, if it holds a single integer
 *     // The result is undefined if this NestedInteger holds a nested list
 *     int getInteger() const;
 *
 *     // Return the nested list that this NestedInteger holds, if it holds a nested list
 *     // The result is undefined if this NestedInteger holds a single integer
 *     const vector<NestedInteger> &getList() const;
 * };
 */

class NestedIterator
{
public:
    NestedIterator(vector<NestedInteger> &nestedList)
    {
        begins.push(nestedList.begin());
        ends.push(nestedList.end());
    }

    int next()
    {
        hasNext();
        return (begins.top()++)->getInteger();
    }

    bool hasNext()
    {
        while (begins.size())
        {
            if (begins.top() == ends.top())
            {
                begins.pop();
                ends.pop();
            }
            else
            {
                auto x = begins.top();
                if (x->isInteger())
                    return true;
                begins.top()++;
                begins.push(x->getList().begin());
                ends.push(x->getList().end());
            }
        }
        return false;
    }

private:
    stack<vector<NestedInteger>::iterator> begins, ends;
};

/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i(nestedList);
 * while (i.hasNext()) cout << i.next();
 */
// @lc code=end
